Tubular cathode for electron discharge devices



July 12, 1938. J. A. SPENCER TUBULAR CTHODE FOR ELECTRON DISCHARGE DEVICES Filed March 4, 1936 FIGZ.

FIGB. l

Patented July 12, 1938 UNITED STATES PATENT OFFICE TUBULAR CATHODE FOR ELECTRON DIS- CHARGE DEVICES John A. Spencer, Newtonville, Mass., assigner, by

mesne assignments, to Metals & Controls Corporation, Attleboro, Mass., a corporation of Massachusetts Application March 4, 1936, Serial No. 67,006

1 Claim.

lar type forV electron discharge devices which is so constructed that its electron emissivity is improved over a considerable length of time; and the provision of a tubular cathode of the class described which may be economically manufactured from readily obtainable materials. Other objects will be in part obvious and in part pointed 'out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplied in the structures hereinafter described, and the scope of the application of which will be indicated in the following claim.

In the accompanying drawing, in which is illustrated one of various possible embodiments of the invention,

Fig. l is a side elevation, partly broken away, of a typical electron emission device;

Fig. 2 is an enlarged side elevation of a tubular cathode;

Fig. 3 is a vertical section of the cathode of Fig. 2, taken substantially along line 3--3 of Fig. 2;

Fig. 4 is a cross-section taken substantially on line 4-4 of Figures 2 and 3; and,

Fig. 5 is a greatly enlarged fragmentary crosssection of a tube.

Similar reference characters indicate corresponding parts throughout the several views of the drawing. 1

Referring now more particularly to Fig. l, there is shown an electron emission device of substantially standard construction. This` comprises an envelope I, which, according to present practice, may be either glass or a metal, an insulating base 2, and connecting prongs 3 eX- tending from the base 2. A stem of insulating material 4, usually glass, is rigidly mounted inside the envelope I, and serves to support the elements of the device.

The number of these so-called elements depend upon the use to which the device is to be put, and varies widely in accordance with present engineering practice. Fig. l shows a socalled three element device, the three elements comprising a cathode 5, a grid Ii, and a plate or anode 1. A heater I is also provided, but since emitting electrons. .described in greater detail hereinafter, which (Cl. Z50-27.5)

it has an indirect function it is not ordinarily considered as an element, These elements are supported in a manner well-known in the art upon the stem 4, and the specic details of their mounting need not be described herein.y

The present invention is concerned more particularly with the construction of the cathode 5. Functionally, the cathode is the portion of the device which is provided for the purpose of It comprises a tube 8, to be has a coating 9 provided on the outside thereof. The coating 9, as is known in the art, comprises substances having the characteristics of emitting large quantities of electrons when suitably heated. A mixture of barium and strontium oxides is frequently employed for this purpose.

In order to emit electrons, the coating 9 must be heated. For this purpose there is mounted centrally in the tube 8 a heater IB (see Fig. 3). The particular heater IE) shown in Fig. 3 is of the twisted hairpin type, which is well-known in the art. The heater I0 is twisted about a refractory rod II, which is enlarged at one end into a circular plug I2 fitting closely into the tube 8. The plug portion I2 is provided with diametrically opposite slots I3 in the bottom of which fit the ends I4 of the heater I0. The closed or hairpin end of the heater I0, indicated by numeral I5, is received in a flat slot I6 formed in a refractory material plug I'I that fits tightly into the upper end of the tube 8.

The plugs IZ and I1 are held in position in the tube 8 by indentations I8 (see Figures 2 and 4) in the tube 8 whichl fit into corresponding depressions !9 in said plugs I2 and I'I.

The heater III, it will be seen, is electrically insulated from the tube 3. In order to connect the tube 8 into the circuit, a metal strip or tab 26 (see Figures l and 2) is connected to the bottom end of said tube 8.

The structure as thus far described is known in the art, and no claim is made to it, except in the following connection:

In prior practice, the tube 8 has usually been made of nickel. I have discovered that if the tube 3, instead of being made of nickel, is made of nickel with an exterior surface impregnation of aluminum, then the electron emissivity of the coating 9 is considerablyV enhanced. This cathode tubing so treated with aluminum, which will hereinafter be termed aluminized tubing, may be prepared in the following manner:

A length of stock nickel tubing is first procured. This is usually of a considerably heavier nature than the ultimate cathode tubing, both as to diameter and as to wall thickness. The outer surface of this nickel tubing is thoroughly cleaned, and metallic aluminum is then sprayed, by methods known in the metal coating art, onto this cleaned surface. Thereafter, the large piece of coating nickel tubing is swaged or drawn down in size until the cathode tubing dimensions are achieved. Following these general principles, the details of the invention have been carried out successfully in the following manner:

A piece of commercially pure nickel tubing about 30 inches long and one inch in outside diameter, which has a wall thickness of about 0.065 inch, is sand blasted in order to clean it and to provide a roughened outersurface. Onto this roughened surface metallic aluminum is sprayed to a thickness of about 0.005 inch, after which the tube is swaged. The swaging tends to drive the aluminum well into the roughened texture of the nickel surface. The swaged piece is then preferably heated in a hydrogen atmosphere furnace to about 760 to 870 C., at which temperature it is believed that some of the aluminum coating infuses into the nickel, the former probably filling the pores of the latter. The heated swaged tube is then subjected to a series of drawing operations, according to ordinary tubing manufacturing practice, which reduces the diameter and wall thickness of the large tube to dimensions suitable` for cathodes of the class concerned. From this stock the individual cathodes may be cut and coated and manufactured into electron discharge devices by methods well-known in the electron discharge device art.

Otherwise identical lelectron discharge devices, one of which has the aluminized nickel cathode tube of the present invention, while the other has ordinary nickel tubing, show electron emissivity, for example, of 110 milliamperes` for the aluminized tubing, and to 85 milliamperes on the ordinary nickel tubing.

Fig. 5 is a greatly enlarged cross-section of an aluminized surface tube, and is believed to correspond to the structure of the tubing, the manufacture of which has just been described. Numeral 2| indicates the pure nickel backing of the tube. Numeral 22 indicates the sprayed aluminum coating on the surface. Numeral 23 indicates a region of infusion or impregnation of the two metals 2| and 22.

If the heating step in the hydrogen furnace is omitted, tubing is obtained which still has improved electron emissivity characteristics. In this event, the infusion of the nickel and aluminum is not believed to take place, at least to as great an extent.

While the spraying procedure has been determined to be the preferred one for providing the aluminum coating on the nickel tubing, other procedure well-known in the art may likewise be used. For example, the aluminum may be electroplated onto the nickel tubing base. Or, aluminum may be mechanically plated, by means of welding or soldering, on the nickel base, or put on by the calorizing process. All of these methods are considered to be comprehended Within the scope of the invention.

From the foregoing it will be seen that the present invention is most particularly concerned with the structure and composition of the cathode tube, and is not concerned with the particular structure of the electron discharge device in which the cathode tube is used. Nor is it important, for purposes of the present invention, how the cathode heater is constructed and mounted in the cathode tube.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in carrying out the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim:

In an electron discharge device, a tubular cathode, a coating of a substance having a high electron emissivity on the outer surface of said cathode, and a heater within said cathode, said cathode comprising a nickel tube having a coating of aluminum less than .005 inch thick on its working surface, said emissive coating surmounting said coating of aluminum.

JOHN A. SPENCER.` 

